Flame propagation characteristics of hydrogen/carbon monoxide/methane (or propane)–air premixed mixtures were studied in a constant pressure combustion chamber with a schlieren system at room temperature and elevated pressures. Unstretched laminar burning velocities and Markstein lengths of various mixtures were obtained by analyzing high-speed schlieren images. Also, the experimentally measured unstretched laminar burning velocities were compared with numerical predictions using the PREMIX code with a H2/CO/C1–C4 mechanism, USC Mech II, developed by Wang et al. . The two data from experiments and predictions show good agreement. The results indicate a significant increase in the unstretched laminar burning velocities with hydrogen enrichment and a decrease with the addition of hydrocarbons, whereas the opposite effects for the Markstein lengths were observed.